Cape Girardeau County
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Armyworms – worms and more worms
Armyworms have marched across many wheat and fescue fields of Cape Girardeau, Scott, Perry and Bollinger Counties leaving bare ground to show for their appetites. Several adjoining counties are also affected.
No one can remember armyworms this bad and the effect is compounded by the dry weather. Millions of worms are common in many fields, they prefer fescue and wheat, but also have been reported eating whole cornfields and attacking alfalfa and other grasses.
If you don’t have armyworms in your fescue pastures, hay or seed crop and your wheat, count yourself lucky and you had better start looking. A small patch of worms, less than an acre in size can move across a 30-acre field in one night, eating all leaves and clipping heads, leaving bare ground and stems. Short hay yields have been further reduced as plants have no leaves and the stems don’t weigh much and are poor quality.
"How long will they be around?" A common question along with "If I don’t do anything, what will happen?" As the current 1/2-inch worms will feed for another 10-14, each worm eating a yard (36 inches) of leaves – 3 fescue plants – doing nothing is inviting the worms to a good lunch for many days. They can and will eat ALL your field and look for more food.
We also have potential for 1 or 2 more generations and the damage could be substantial based on current numbers as each adult can lay over 100 eggs = more worms.
Look carefully, in very early morning and late afternoon – the small worms, especially, take siestas under the lower leaves, stalks and residue, even in ground cracks, during the daytime – and feed at night. Look away from field edges, the sneaky rascals often leave a strip uneaten along roadsides, making windshield scouting inaccurate.
Stripped wheat in the dough stage can make some grain, but the grain will be shriveled and have a low-test weight. More immature wheat would be a prime candidate for drilling in soybeans, as yield will be very low—may not pay combining and be hard to market.
Fescue seed fields and pastures
Treatment for this pest is justified when an average of four or more non-parasitized, half-grown or larger worms per square foot are present during late spring and before more than 2 to 3% of seed heads are cut from stems by this pest. If an insecticide application is necessary on fescue or grass pastures, use one of the following insecticides.
Insecticide Product rate/acre Preharvest/grazing interval
Malathion 57% EC 2 pts 0 days, remove cows during application
Penncap-M * 2 to 3 pts. 15 days for harvest or graze
Sevin XLR Plus 2 to 3 pts. 14 days ground application, 0 days air application
Confirm 2F 6-8 oz. 0 days – allow to dry – good on large worms
* designates a restricted use pesticide
Follow all label directions, precautions, and restrictions
Pounce
If pastures have one or more of the following plants, then it is legal to spray with Pounce according to the alfalfa label:
Alfalfa Crotalaria Purple prairieclover
Burclover Crown vetch Rough pea
Clover, Alyce Globemallow Sweet clover
Clover, Hop Gumweed Tapertip hawksbeard
Clover, Red Kochia (A pigweed) Threadleaf sedge
Clover, White Lespedeza Vetch
If using 0 – 4 oz., there is a 1-day preharvest/pregrazing period.
If using 4 or more oz., there is a 14-day preharvest/pregrazing period.
Armyworms in Wheat Fields
In wheat, treatment for true armyworm is justified when an average of four or more non-parasitized, half-grown or larger worms per square foot are present during late spring and before more than 2 to 3% of seed heads are cut from stems by this pest. If an insecticide application is necessary on wheat, use one of the following insecticides:
Insecticide Product rate/Acre
Penncap-M * 2 to 3 pts.
Sevin XLR Plus 2 to 3 pts.
Warrior * 2.56 to 3.84 oz.
* designates a restricted use pesticide
Follow all label directions, precautions, and restrictions.
Armyworms in Corn
A small number of corn infestations have been reported but damage has been devastating. Control of armyworm in corn is justified if 25% or more of corn seedlings are significantly damaged through foliage feeding by larvae. Insecticides labeled for control of true armyworm in field corn include:
Insecticide Product rate/Acre
Ambush * 6.4 to 12.8 oz.
Asana XL * 5.8 to 9.6 oz.
Lorsban 4E 1 to 2 pt.
PenncapM * 2 to 3 pt.
Pounce 3.2EC * 4 to 8 oz.
Sevin XLR Plus 1 to 2 qt.
* designates a restricted use pesticide
Follow all label directions, precautions, and restrictions.
Reporting Losses
We are trying to establish a base of losses due to armyworms. If you have had armyworm problems, please send me a note with number of acres owned, number of acres with armyworm losses, degree of damage or yield reduction, and number of acres sprayed for wheat, pasture and hay. I plan to use this data to lobby for assistance. The more reported, the better the case can be presented. Thank you.
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University of Missouri Extension Cape Girardeau County capeco@missouri.edu 573-243-3581 Last revised: 08/14/2008 |
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